The present invention relates to rotary printing presses, and more particularly to apparatus for automatically skewing one cylinder of the rotary printing press, such as a form roller, in response to skewing of another cylinder thereof, such as a plate cylinder.
In rotary printing presses, particularly mutlicolor web printing presses, it is desirable to provide an adjustment for skewing or cocking of the plate cylinder axis relative to the axis of its coacting blanket cylinder. This is because of possible skew in the mounting of the printing plate on the plate cylinder, or skew of the image on the printing plate. Either of these types of skew can produce misalignment of the printed image produced on the web by one printing couple with printed images printed by other printing couples. By skewing the axis of the plate cylinder this misalignment can be eliminated. When the axis of the plate cylinder of a rotary printing press is skewed relative to the axis of its cooperating blanket cylinder, it is known to also skew a form roller which cooperates with the plate cylinder to maintain the axes thereof in substantial parallelism. Also, the form roller in a printing press, as is well known, may be moved between a thrown-off position and a thrown-on position. In the thrown-on position the form roller is in a liquid transfer relationship with a plate on the plate cylinder. In the thrown-off position the form roller is spaced from the plate cylinder and in a non-liquid transfer relationship with a plate on the plate cylinder.
The patent to James, U.S. Pat. No. 3,691,956, illustrates a typical mechanism for moving the ink form rollers between thrown-on and thrown-off positions. Specifically, the patent illustrates the biasing of form roller mountings against rockable cam rings. The cam rings are rotated in order to affect throw-on and throw-off of the form roll.
There are known mechanisms which provide for movement of a form roll between thrown-on and thrown-off positions and also provide for skewing the axis of the ink form roll relative to the axis of the blanket cylinder in response to skew of the plate cylinder axis relative to the blanket cylinder axis. Typical of these patents are U.S. Pat. Nos. 3,065,690; 3,167,025; 3,208,377 and 3,817,173.